Aluminum alloy and die casting method

ABSTRACT

An aluminum alloy used for a die casting process and a method for casting the aluminum alloy are provided. The aluminum alloy exhibits excellent internal quality, high elongation, and high strength. The aluminum alloy includes 6.0 to 9.0 mass % of Si, 0.4 to 0.8 mass % of Mg, 0.25 to 1.0 mass % of Cu, 0.08 to 0.25 mass % of Fe, 0.6 mass % or less of Mn, 0.2 mass % or less of Ti, and 0.01 mass % or less of one element selected from the group consisting of Sr, Sb, Ca, and Na, with the balance being Al and unavoidable impurities.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of International Patent ApplicationNo. PCT/JP2014/084505, having an international filing date of Dec. 26,2014, which designated the United States, the entirety of which isincorporated herein by reference. Japanese Patent Application No.2014-071281 filed on Mar. 31, 2014 is also incorporated herein byreference in its entirety.

TECHNICAL FIELD

The present invention relates to an aluminum alloy that is used for adie casting process (aluminum die casting process), and a castingmethod.

BACKGROUND ART

A die casting process has high productivity, and is used in a widevariety of fields in which aluminum parts (e.g., automotive parts andmechanical parts) are used.

An aluminum alloy that is equivalent to a Japanese Industrial Standards(JIS) ADC12 alloy is generally used as an aluminum alloy used for thedie casting process.

The JIS ADC12 alloy exhibits excellent castability. However, since aproduct obtained by subjecting the JIS ADC12 alloy to the die castingprocess has a coarse needle-like metal microstructure, fracture easilyoccurs from the precipitates, and it is difficult to obtain sufficientstrength.

Therefore, it is necessary to increase the thickness of the product fromthe viewpoint of safety.

When a T6 treatment is employed to improve strength, an increase in costoccurs.

Moreover, when producing a product that partially has a large thickness,deformation may occur due to thermal strain.

Japanese Patent No. 4970709 discloses an aluminum alloy that is used fora die casting process and exhibits high elongation in an as-cast state.In Japanese Patent No. 4970709, it is indispensable to add molybdenum tothe aluminum alloy.

SUMMERY OF THE INVENTION Technical Problem

An object of the invention is to provide an aluminum alloy that is usedfor a die casting process, and exhibits excellent internal quality, highelongation, and high strength, and a method for casting the same.

Solution to Problems

An aluminum alloy according to one aspect of the invention includes 6.0to 9.0 mass % of Si, 0.4 to 0.8 mass % of Mg, 0.25 to 1.0 mass % of Cu,0.08 to 0.25 mass % of Fe, 0.6 mass % or less of Mn, 0.2 mass % or lessof Ti, and 0.01 mass % or less of one element selected from the groupconsisting of Sr, Sb, Ca, and Na with the balance being Al andunavoidable impurities.

A casting method according to another aspect of the invention includespouring molten metal of an Al—Si—Cu—Mg-based aluminum alloy into a shotsleeve of a die casting machine, and filling a mold cavity of acenter-gate die with the molten metal at a gate speed of 1 m/sec or lessso as to produce a laminar flow.

A release agent is normally applied to the inside of the mold cavity orthe like when implementing a die casting process. A solution-typerelease agent (e.g., oily release agent or water-soluble release agent)may be used when implementing the casting method.

In the invention, it is preferable to apply a powdery release agent tothe inside of the mold cavity.

A powdery release agent suppresses a decrease in die temperature.

The above alloy composition is selected for the reasons described below.

Si

The Si content must be 6 mass % or more in order to obtain fluidityduring casting. In the invention, the Si content is set to achieve ahypo-eutectic region.

When the Si content is set to achieve a hypo-eutectic region, theprecipitation of coarse Si primary crystals and fracture therefromrarely occur. Therefore, it is possible to obtain an elongation that isrequired to provide the aluminum alloy with good mechanical properties.

Therefore, the Si content is preferably set to 6.0 to 9.0 mass %.

Mg and Cu

Mg and Cu are required to provide the aluminum alloy with high strength.The Mg content is preferably set to 0.4 to 0.8 mass %, and the Cucontent is preferably set to 0.25 to 1.0 mass %.

Fe

Fe improves toughness when the Fe content is low. If the Fe contentexceeds 0.25 mass %, a decrease in ductility may occur.

Fe is easily mixed as impurities. It is necessary to increase the purityof the master alloy (i.e., an increase in cost occurs) in order toreduce the Fe content.

Therefore, the Fe content is preferably set to 0.08 to 0.25 mass %.

Mn

The addition of a small amount of Mn is effective for preventing thealloy from burning and sticking together with the mold during the diecasting process.

When Mn is added to the aluminum alloy, the Mn content is preferably setto 0.6 mass % or less.

Sr, Sb, Ca, and Na

The addition of a small amount of Sr, Sb, Ca, or Na (modifier) iseffective for achieving the refinement of eutectic silicon.

It is preferable to add one element among Sr, Sb, Ca, and Na in ratio of0.01 mass % or less.

Ti

Ti is effective for achieving the refinement of crystal grains duringcasting. Ti may be added in a ratio of 0.2 mass % or less.

A small amount of B is included in the aluminum alloy when Ti is addedto the master alloy.

When the aluminum alloy having the above structure is used, an Fmaterial obtained by air-cooling the product obtained by the die castingprocess, or a T5 material obtained by tempering the F material exhibitsimproved strength, and it is unnecessary to use a T6 treatment thatincreases cost.

It is also effective to reduce internal defects of the cast product inorder to reduce the thickness of the cast product.

Therefore, it is preferable to pour molten metal of an Al—Si—Cu—Mg-basedaluminum alloy into a shot sleeve of a die casting machine, and fill themold cavity of a center-gate die with the molten metal at a gate speedof 1 m/sec or less so as to produce a laminar flow.

The type of the die casting machine is not particularly limited as longas the center gate can be provided to the die.

It is preferable to maintain the die temperature when casting a producthaving a small thickness. Therefore, it is preferable to use a powderyrelease agent that exhibits thermal insulation properties rather than awater-soluble release agent.

In the invention, Zn, Ni, Sn, Cr, and the like are considered to beunavoidable impurities. These elements may be included in the aluminumalloy each in a ratio of 0.03 mass % or less.

Advantageous Effects of Invention

The aluminum alloy having the chemical composition according to theinvention exhibits fluidity due to Si, exhibits improved strength due toMg and Cu, has a lower Fe content as compared with a known aluminumalloy, and exhibits improved elongation through modification with Sr andthe like. Therefore, the aluminum alloy exhibits high strength withoutthe need for a T6 treatment.

Therefore, it is possible to reduce or suppress an increase in cost thatmay occur when a T6 treatment is used, and eliminate the occurrence ofthermal strain due to quenching, so that the dimensional accuracy of aproduct having a small thickness can be improved.

It is possible to improve internal quality by employing the laminar flowdie casting process. It is possible to further improve internal qualityby employing the center-gate die design.

Note that it is preferable to provide an intermediate die between amovable die and a stationary die when casting an undercut product.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1A and 1B illustrate the chemical components of aluminum alloyssubjected to evaluation, and the evaluation results.

FIGS. 2A and 2B illustrate a photograph of the structure of the aluminumalloy obtained in Example 1.

FIG. 3A illustrates a photograph of the structure of the aluminum alloyobtained in Comparative Example 1, FIG. 3B illustrates a photograph ofthe structure of the aluminum alloy obtained in Comparative Example 6,and FIG. 3C illustrates a photograph of the structure of the aluminumalloy obtained in Comparative Example 10.

FIGS. 4A to 4D illustrate an example of the shape of a cast product.

FIG. 5 schematically illustrates the principle of a die casting process.

FIG. 6 illustrates an example of a die structure in which anintermediate die is provided between a stationary die and a movable die.

DESCRIPTION OF EMBODIMENTS

The aluminum alloy and the casting method according to the invention arefurther described below.

Molten metal of each aluminum alloy including the chemical componentslisted in FIG. 1A (having the composition listed in FIG. 1A) wasprepared, and subjected to a die casting process to produce a product.It may be possible to add one element among Sb, Ca, and Na in ratio of0.01 mass % or less instead of Sr in FIG. 1A, since Sb, Ca, or Na hasthe same effect as Sr.

A JIS No. 14 proportional test piece was cut from the product, and themechanical properties were evaluated using the test piece.

The die casting process was performed at a gate speed as low as 1 m/secor less so as to produce a laminar flow.

A heat treatment (T5) was then performed at 180° C. for 180 minutes.

FIG. 6 illustrates an example of the die structure.

The evaluation results are listed in FIG. 1B (table).

In FIG. 1B, the target values are specified for the mechanicalproperties (tensile strength, yield strength (0.2%), and elongation).

In Examples 1 to 12, the content of each chemical component was set tobe within the specific target range, and good mechanical properties wereobtained.

Since good mechanical properties were obtained by the T5 heat treatment,it is possible to reduce cost.

In Comparative Examples 1 to 3, the elongation was lower than the targetvalue since a modification was not applied.

In Comparative Example 2, good strength was obtained by a T6 treatment,but the elongation was lower than the target value, and an increase incost occurs due to the T6 treatment.

In Comparative Example 4, good mechanical properties were obtained.However, since a T6 treatment was applied, an increase in cost occurs.

In Comparative Example 5, good mechanical properties were not obtainedby a T5 treatment since the Cu content was low.

In Comparative Example 6, the elongation was lower than the target valuesince a modification was not applied, and the Cu content and the Sicontent were outside the specific ranges.

Since the Mn content was high in Comparative Example 6, coarsecrystallized products were formed, and the elongation was lower than thetarget value.

Since a T6 treatment is required in Comparative Example 6, an increasein cost occurs.

In Comparative Example 7, the elongation was lower than the target valuesince a modification was not applied, and the Cu content and the Sicontent were outside the specific ranges.

Since the Mn content was high in Comparative Example 7, coarsecrystallized products were observed, and the elongation was lower thanthe target value.

In Comparative Example 8, since the Cu content was outside the specificrange, and the Mn content was high, coarse crystallized products wereobserved, and the elongation was lower than the target value.

In Comparative Example 9, good mechanical properties were not obtainedsince the Cu content was low.

In Comparative Example 10, a T6 treatment was applied (i.e., an increasein cost occurs).

In Comparative Example 11, good mechanical properties were not obtainedsince the Mg content was low.

In Comparative Example 12, a T6 treatment was applied (i.e., an increasein cost occurs).

FIGS. 2A and 2B illustrate a photograph of the metal structure obtainedin Example 1, FIG. 3A illustrates a photograph of the metal structureobtained in Comparative Example 1, FIG. 3B illustrates a photograph ofthe metal structure obtained in Comparative Example 6 and FIG. 3Cillustrates a photograph of the metal structure obtained in ComparativeExample 10.

It was confirmed that eutectic silicon was refined when the aluminumalloy according to the invention was used.

The die structure is described below.

As illustrated in FIG. 5 (schematic view), a cavity 13 is formed by astationary die 11 and a movable die 12. When implementing the diecasting process, molten metal is poured into a sleeve 14, and injectedinto the cavity 13.

Die casting machines are classified into a horizontal die castingmachine and a vertical die casting machine. A horizontal die castingmachine is mainly used at present from the viewpoint of productivity andthe like.

Horizontal die casting machines are classified into an under-gate diecasting machine (in which the gate is provided on the lower side) (seeFIG. 5) and a center-gate die casting machine (in which the gate isprovided at the center).

For example, when producing a cylindrical product and the likeillustrated in FIGS. 4A to 4D (cross-sectional views), it is possible tosuppress the occurrence of segregation and obtain excellent internalquality by injecting the molten metal into the cavity at a positioncorresponding to the center of the product (see the die structureillustrated in FIG. 6).

Therefore, it is preferable to use a center-gate die, and fill thecavity with the molten metal at a gate speed (i.e., the speed at whichthe molten metal passes through the runner gate of the die) of 1 m/secor less so as to produce a laminar flow.

Note that a center-gate die casting machine in which the gate isprovided at the center may also be used (not illustrated in thedrawings). When a die structure is formed so that an intermediate die 15is provided between the stationary die 11 and the movable die 12 (seeFIG. 6), it is possible to form a center-gate die having a center gate11 a using an under-gate die casting machine (in which the gate isprovided on the lower side) by providing a runner between the stationarydie 11 and the intermediate die 15.

It is possible to produce products having various shapes (see FIGS. 4Ato 4D) by utilizing such a die structure that includes three split dies.

INDUSTRIAL APPLICABILITY

The aluminum alloy according to the invention exhibits high strengthwithout the need for a T6 treatment and can be applied to variousautomotive parts and various mechanical parts. The aluminum alloyaccording to the invention exhibits excellent die castability, andachieves high productivity.

What is claimed is:
 1. An aluminum alloy comprising 6.0 to 9.0 mass % ofSi, 0.4 to 0.8 mass % of Mg, 0.25 to 1.0 mass % of Cu, 0.08 to 0.25 mass% of Fe, 0.6 mass % or less of Mn, 0.2 mass % or less of Ti, and 0.01mass % or less of one element selected from a group consisting of Sr,Sb, Ca, and Na, with the balance being Al and unavoidable impurities. 2.A method for casting an aluminum alloy comprising: pouring a moltenmetal of an Al—Si—Cu—Mg-based aluminum alloy into a shot sleeve of a diecasting machine; and filling a mold cavity of a center-gate die with themolten metal at a gate speed of 1 m/sec or less so as to produce alaminar flow.
 3. The method as defined in claim 2, wherein a powderyrelease agent is applied inside the mold cavity.
 4. A method for castingan aluminum alloy comprising: pouring a molten metal of anAl—Si—Cu—Mg-based aluminum alloy into a shot sleeve of a die castingmachine; and filling a mold cavity of a center-gate die with the moltenmetal at a gate speed of 1 m/sec or less so as to produce a laminarflow, wherein the Al—Si—Cu—Mg-based aluminum alloy includes 6.0 to 9.0mass % of Si, 0.4 to 0.8 mass % of Mg, 0.25 to 1.0 mass % of Cu, 0.08 to0.25 mass % of Fe, 0.6 mass % or less of Mn, 0.2 mass % or less of Ti,and 0.01 mass % or less of one element selected from a group consistingof Sr, Sb, Ca, and Na, with the balance being Al and unavoidableimpurities.
 5. The method as defined in claim 4, wherein a powderyrelease agent is applied inside the mold cavity.